The invention pertains to cutting tools used in excavating earth formations wherein a block on a driven body, such as a drum or a wheel or a blade, contains the cutting tool having a hard tip at the forward end thereof. More specifically, the invention pertains to the shape of the hard tip.
Cutting tools are a consumable component of the overall apparatus used to break an earth formation (e.g. rock, asphalt, coal, concrete, potash, trona) into a plurality of pieces which comprise abrasive cuttings. For example, a road planing machine uses cutting tools which mount in blocks on a driven drum. An engine in the road planing apparatus drives the drum. The rotation of the drum causes the cutting tools to impinge upon a road surface, such as asphalt. The result is to break the road surface into small pieces thereby creating abrasive cuttings. The abrasive cuttings are removed thereby preparing the roadway for resurfacing.
The typical cutting tool comprises an elongate tool body (typically made of steel) with an axially forward end and an axially rearward end. The cutting tool contains a means for retaining the tool in the bore of the block. Such a retention means may retain the cutting tool in such a fashion that it is rotatable with respect to the block or it is non-rotatable with respect to the block. The block mounts on a rotatable drum driven by the overall apparatus. A hard cutting tip, which may be made from a cemented tungsten carbide (WC-Co alloy) having a cobalt content ranging from about 5 to about 13 weight percent, affixes to the forward end of the cutting tool. Typically, one brazes the hard cutting tip to the tool body.
The hard cutting tip is the component of the cutting tool that first impinges upon the earth formation or substrate. Thus, there has been an interest in the shape of the hard cutting tip, and the influence the shape of the hard cutting tip has on the performance of the cutting tool.
There have been three basic concerns associated with a hard cutting tip. One concern has been to provide a hard cutting tip that easily penetrates and cuts the earth formation. Another concern has been to provide a hard cutting tip that has satisfactory strength so as to be able to endure throughout a cutting application without failure through catastrophic means such as fracture. Another concern has been to provide a hard cutting tip that helps protect the steel tool body, as well as the joint between the hard cutting tip and the steel tool body, from erosion by the abrasive cuttings, i.e., so-called "steel wash".
The hard cutting tip typically has been made from a powder via powder metallurgical techniques. In the manufacture of a part via powder metallurgical techniques, it is important that the powder move easily and uniformly during compaction so that the pressed, pre-sintered part has a uniform powder density. It is typical that a pre-sintered compact with a more uniform powder density will have less of a tendency to form regions having density variations or voids which can reduce the overall strength of the tip. In the past, hard cutting tips for cutting tools, wherein the hard cutting tip has been the product of powder metallurgical techniques, have at times experienced the presence of some degree of cracks or voids. As mentioned above, these cracks or voids have been typically due to a non-uniform powder density in certain volumes of the tip geometry. In some circumstances, the presence of surfaces that restrict the flow of powder contribute to such a non-uniform powder density in the pressed, pre-sintered part. Thus, it would be highly desirable to provide an improved cutting tool with a hard cutting tip that presents surfaces that do not restrict, or at least reduce the restriction to, the movement of powder to all volumes of the tip during the pressing thereof.
It has been the case that surfaces of the part which are somewhat perpendicular to the longitudinal axis of the part can create obstacles to powder flow, and hence, lead to a non-uniform powder density in the pressed pre-sintered tip. It would thus be highly desirable to provide an improved cutting tool with a hard cutting tip that presents a forward portion with a geometry that reduces the number of, or even eliminates all, surfaces that are generally perpendicular to the longitudinal axis of the hard cutting tip.
In some instances, the density of the powder in the larger dimension portions of the hard cutting tip have been greater than average. This is due to the restriction of powder moving from the larger dimension portions of the hard cutting tip during pressing. Thus, it would be highly desirable to provide an improved cutting tool wherein the powder density in the pressed, pre-sintered compact for the hard cutting tip has a generally uniform density, or at least a more uniform density than has been the case with earlier tip geometries.
The following patents and documents show cutting tools with hard cutting tips presenting specific geometric shapes. For example, some patents or documents show a hard cutting tip with a cylindrical section axially rearwardly of the conical tip section. Some patents or documents show a middle section of the hard cutting tip having a geometry with a contour.
U.S. Pat. Nos. 4,725,099 and 4,865,392 to Penkunas et al. each shows a cutting tool having an insert. The insert has a conical tip section, an integral axially rearward cylindrical section, an axially rearward integral frusto-conical section, an axially rearward integral fillet section and an axially rearward integral base section.
U.S. Pat. No. 4,938,538 to Larsson et al. and European Patent No. 0 122 893 to Larsson et al. each show a cutting tool with an insert. The insert has a conical tip section, an integral cylindrical section axially rearward of the tip portion, an integral arcuate section axially rearward of the cylindrical portion, an integral flange section axially rearward of the arcuate portion and an integral section by which the cutting insert mounts in a socket in the steel tool body.
Kennametal Drawing No. DEV-C-1736 depicts a cemented carbide tip for use in conjunction with a rotatable cutting tool. The tip presents a conical tip section and an integral frusto-conical intermediate section with a scallop or recess contained therein.
U.S. Pat. No. 4,729,603 to Elfgen shows a hard insert that presents a plurality of grooves filled in with a material that is softer than the remainder of the hard insert.
U.S. Pat. No. 5,131,725 to Rowlett et al., assigned to the assignee (Kennametal Inc. of Latrobe, Pa.) of the present patent application, shows a cemented carbide tip for a rotatable cutting tool. The geometry of the cemented carbide tip presents a trio of radially extending fins that transcend a cylindrical section to a concave section to a frusto-conical section.
U.S. Pat. No. 3,356,418 to Healey et al. shows a hard insert with a plurality of longitudinal splines.
Soviet Authors Certificate No. 751,991 for a MINING MACHINE PICK WITH HARD METAL TIP shows a hard metal tip. The tip presents a plurality of conical surfaces (7) that intersect to form a plurality of ribs. Each rib appears to travel from near the axially forward portion of the tip to the axially rearward portion of the hard metal tip.
Soviet Authors Certificate No. 825,924 shows a hard insert with ribs that engage slots in the steel body of the tool.
German Publication No 3510072 shows a hard insert having longitudinal grooves used to facilitate solder distribution in the attachment of the hard insert to the tool body.